Remote control system



Dec. 23, 1947. BOND REMOTE CONTROL SYSTEM Filed Oct. 1, 1942 DUNHLD Bum) 55.5% 9 323: 8% m a r. n q q sum k 8$ mm "5% A mwm w a P3 mw M4 7 wzqm mxmuqfi 5&3 3M3 03mm mw -Exi NNI g w 4 E a N E s R 0 n m du Rwn u I .l ilu m Ex 45 k3 aim m gfiq mmbt 08 k... I I i l I I t I I I i l I I I I I l- I I I ll\ NEE} (Ittorneg Patented Dec. 23, 1947 REMOTE CONTROL SYSTEM Donald S. Bond, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application October 1, 1942, Serial No. 460,339

7 Claims.

This invention relates to remote control systems, and more particularly to an improved system requiring but a single telephone circuit or radio link between the control member and the controlled device.

It is an object of the invention to provide an improved method of and means for transmitting the signals required to establish control of the' position of a movable object in response to the position of a control member.

Another object is to provide an improved method of and means for deriving a control signal including a modulated carrier, in which the phase relationship between certain components of the signal corresponds to the intelligence to be transmitted.

A further object is to provide an improved method of and means for converting a signal comprising two voltages of equal frequency and varying phase relationship into a signal which may be transmitted through a single channel,

and reconverting said signal after transmission.

. Y 2 v phase shifter 3. The output of the phase shifter 2|" is applied toa phase detector 23. The output of the filter I5 is applied through an amplifier 25 to the phase detector 23. The output of the detector 23 is connected through a low pass filter 21 to a balanced modulator 29. Voltage from an alternating current power line 3| is applied to the modulator 29 through a phase adjuster 33.

These and other objects will become apparent to those skilled in the art upon consideration of the following description of the invention, with reference to the'accompanying drawing, of which Fig. 1 is a schematic block diagram of an embodiment of the invention, Fig. 2 is a circuit diagram of a balanced modulator, Fig. 3 is a circuit diagram of a bridge type mixer, and Fig. 4 is a circuit diagram of a phase discriminator.

Referring to Fig. 1, a control device, of which the angular position is to be reproduced at a remote point, is mechanically connected to a phase shifter 3. An oscillator 5, operating at a frequency of, for example, 60 cycles per second, is connected to the input of the phase shifter 3. The device 3 is constructed like a goniometer or in any suitable manner so that it provides a continuous change of phase upon rotation of its control shaft. The output of the phase shifter is applied to a balanced modulator I. A second oscillator 9- operating at a frequency of, for example, 1000 cycles per second is also connected to the balanced modulator. The output of the balanced modulator I is applied to a mixer circuit II, which is also connected to the oscillator 5.

The output of the mixer I I is transmitted over a telephone circuit or radio link to the receiver station, where the motion of the device I is to be duplicated by a load device 39. The transmitted signal is applied to filters I3 and I5. The filter I3 is connected to a demodulator I! which is connected in turn through an amplifier I9 to a phase shifter 2| similar in construction to the The output of the modulator 29 is connected to an amplifier 35. A two phase motor" 31 is provided with one phase connected to the output of the amplifier 35 and the other phase connected to the power line 3|. The motor 31 is mechanically connected to the phase shifter 2| and to the load device 39.

The operation of the system is as follows: The output of the oscillator 5 is shifted in phase by the device 3 to an extent depending on the position of the control member I. The cycle output of the phase shifter 3 is combined in the balanced modulator I with the 1000 cycle output of the oscillator 9. The 60 cycle component is suppressed by the action of the balanced modulator, thus providing an output comprising the 1000 cycle sidebands of a 60 cycle carrier, namely, 940 cycles and 1060 cycles, as well as the 1000 cycle modulation. The phase of the sideband frequencies with respect to a fixed reference is similar to that of the output of the phase shifter 3 with respect to that of the oscillator 5. Phase reference voltage is provided by the oscillator 5, and is added to the products of the modulator Tin the mixer circuit I I. The function of the mixer II is merely that of superposition, not modulation. The mixer I I is arranged to isolate the oscillator 5 from the modulator 'I to prevent interaction between their outputs, as more fully described hereinafter. The output of the mixer II thus comprises components at 940 cycles, 1000 cycles, 1060 cycles, and a fixed-phase component at 60 cycles.

The higher frequency components areseparated at the receiver station by the filter I3. The demodulator I'I regards these components as a 1000 cycle carrier with 60 cycle sidebands at 940 and 1060 cycles, and accordinglyprovides a 60 cycle output. This 60 cycle output varies in phase with the variations in phase of the output of the phase shifter 3 at the transmitter] The 60 cycle constant phase component of the transmitted signal is separated by the filter I5,

amplified by the amplifier 25. and applied to the phase detector 23. The variable phase 60 cycle,

' plied to the two motor windings.

er 2| to the phase detector 23. The output of the phase detector 23 is a D.-C. voltage, having a magnitude related to the magnitude of the phase displacement between the output of the phase shifter and the reference phase voltage, and a polarit depending upon the direction of said displacement. This voltage is conducted through the filter 21 to remove any remaining ripple from the 60 cycle inputs, and controls the balanced modulator 29, varying the magnitude and polarity of the voltage derived from the power line 3| through the phase adjustor 33. It should be noted that the power line frequency may be entirely independent of the frequency of the local oscillator 5. In any event the power line frequency output of the balanced modulator 29 is amplified by the amplifier 35 and used to energize the winding 4| of the motor 31. The motor winding 43 is energized directly from the power line. The phase adjustor 33 is adjusted to provide quadrature phase relationship between the voltages ap- The motor 31 runs in the proper direction to drive the phase shifter 2| toward a position such that its output is 90 out of phase with the reference phase voltage. At this point the output of the phase detector becomes zero, the power line frequency output of the modulator 29 likewise drops to zero, and the motor winding 42 is de-energized, stopping the motor. Upon further displacement of the control device I, the same action occurs and the phase shifter 2| is again rotated to stop the motor. Consequently, the controlled device 39, being mechanically connected to the phase shifter 2| and the motor 31, is maintained in positional agreement with the control device I.

Fig. 2 shows a circuit which may be used for the balanced modulators T and 29. A pair of tubes 4| and 43 are connected in push-pull to a load circuit such as the primary 45 of an output transformer. A pair of input terminals 41 and 49 is connected to the grids of the tubes 4| and 43, and two resistors and 53 are connected in series between the two grids. A second pair of input terminals 55 and 51 is connected between the junction of the resistors 5| and 53 and the common grid return circuit of the tubes 4| and 43.

When no input is applied to the terminals 41 and 49, no voltage appears in the output circuit, regardless of the input to the terminals 55 and 57, because the individual outputs of the two tubes are applied to the load in phase opposition. However if a voltage is applied to the terminals 41 and 49, it is amplified and applied to the load, and at the same time modulates any input to the terminals 55 and 51. This action occurs because the circuit is periodically unbalanced, first in one direction and then in the other by the input to the terminals 41 and 49. In the circuit of Fig. 1, the output of the oscillator 9 is connected to the terminals 4'1 and 49 of the modulator l, and the output of the phase shifter 3 is connected to the terminals 55 and 51. The modulator 29 has its terminals 55 and 51 connected to the phase adjuster 33 and the terminals 41 and 49 to the filter 27.

Fig. 3 shows a suitable circuit for the mixer The center tapped secondary 5| of a transformer 59 is connected to the primaries 83 and 65 of a pair of transformers El and 68 to form a balanced bridge circuit. A network 52 is connected to the transformer 68 to balance the impedance of the load on the transformer 51. A voltage applied to the primary of the transsum of the two input voltages.

former 59 produces no output at the terminals 69 and H, and a voltage applied to these terminals produces no effect at the primary of the transformer 59. The voltage across the primary 65 of the transformer 61 is proportional to the This circuit or some equivalent thereof is necessary in the system of Fig. l to prevent plate circuit modulation in the modulator l by voltage from the oscillator 5.

Fig. 4 shows the circuit of the phase detector 23 of Fig. 1. Two diodes l3 and 15 are connected as shown between center tapped input and output circuits l1 and I9. The variable phase signal voltage is applied to the diodes in push pull through a transformer 9|, and the constant phase reference voltage is-applied to the two diodes in phase between the center taps of the input and output circuits. When the two inputs are in phase at one diode, they are out of phase at the other, thus causing current to flow through the corresponding section of the output circuit, toward the center tap. When the two inputs are in quadrature, no output voltage is produced. Thus the device provides a unidirectional output voltage, of magnitude and polarity depending on the phase relationship between the two input voltages.

It is usually necessary, in a control system of the follow-up type, in which the driving motor operates to reduce the control signal to zero value, to incorporate some means to prevent hunting, Although such anti-hunting system has been omitted from the above description for the sake of clarity, one suitable system is described in U. S. Patent No. 2,208,623 to D. S. Bond.

Thus the invention has been described as an improved remote control system. A low frequency voltage is generated and shifted in phase to correspond to the control information to be transmitted. The shifted voltage is then modulated, the shifted low frequency carrier is suppressed, and replaced by the original constant phase low frequency voltage. transmitted to the control station, when the constant phase voltage is separated from the variable phase modulation. The modulation is detected, providing variable phase low frequency voltage. This voltage is compared with the constant phase low frequency component of the signal, providing a control voltage which is used to control an electric motor, A. single signal channel suffices to carry all of the necessary information, and in fact may be used simultaneously for a plurality of systems of the type described, operating with different modulation frequencies.

I claim as my invention:

1. The method of transmitting control information including the steps of generating an alternating voltage, shifting the phase of said voltage in response to the information to be transmitted, generating a second alternating voltage of substantially higher frequency than said first alternating voltage, modulating said phase shifted voltage in opposite phases by said second alternating voltage to provide two modulated signals whose carriers are degrees out of phase with each other and whose respective side bands are in phase with each other, combining said modulated signals to cancel said carriers and provide a suppressed carrier signal comprising only said side band signals, adding to said suppressed carrier signal a constant phase alternating voltage of the same frequency as said phase shifted voltage, transmitting the resultant combined signal,

This signal is:

receiving said transmitted signal, separating the constant phase component of said signal from the variable phase sideband components thereof, demodulating said variable phase components to provide a variable phase alternating voltage, combining said variable phase voltage with said constant phase signal component to produce a direct current related in magnitude and polarity to the difference in phase of said variable phase voltage and said constant phase signal component, shifting the phase of said variable phase component in response to said direct current so as to reduce said phase difference to zero, and deriving control information in response to the extent of said phase shift of said variable phase component.

2. The method of transmitting a variable phase control voltage and a constant phase reference voltage through a single channel including the steps of generating a modulating voltage of substantially different frequency from said firstmentioned voltages, modulating one of said firstmentioned voltages in opposite phases by said modulating voltage to provide two modulated signals whose carriers are in phase opposition to each other and whose corresponding side bands are in phase with each other, combining said modulated signals to cancel said carriers and provide a suppressed carrier signal comprising only said side-band signals, adding the other of said two first-mentioned voltages to said suppressed carrier signal, to provide a combined signal transmitting said combined signal, receiving said combined signal, separating said suppressed carrier signal component from said added voltage component, demodulating said suppressed carrier signal component to produce a voltage similar to the carrier component which was suppressed, combining said last mentioned voltage with said added voltage component, and deriving a control signal from the product of said combination.

3. A control system including a source of relatively low frequency. alternating current, a control member arranged toshift the phase of said alternating current, a source of relatively higher frequency alternating current, a balanced modulator arranged to modulate said lower frequency current withsaid higher frequency current, a mixer connected to combine the output of said balanced modulator with that of said source of low frequency current, means for transmitting and means for receiving the combined signal output of said mixer, filter means arranged to separate the low frequency component from'the higher frequency components of said combined signal, a demodulator arranged to derive from said higher frequency components a variable phase low frequency voltage, a phase detector connected to respond to said variable phase voltage and said low frequency signal component, means responsive to the output of said phase detector to shift the phase of said variable phase component soas to produce zero output from said phase detector, and means for operating a controlled member as a function of said phase shift.

4. A system for reproducing at a remote point the phase relationship between a variable phase control voltage and a constant phase reference voltage, including an auxiliary source of alternating current, balanced modulator means for modulating one of said voltages with the output of said auxiliary source, a mixer arranged to combine the other of said voltages with the output of said modulating means, means for transmitting and receiving through a single channel the combined output signal of said mixer, filter means for separating the modulated component of said signal from the remainder thereof, and demodulator means arranged to derive from said component a modulation voltage corresponding to one of said original voltages.

5. A remote control system including means for deriving a variable phase control signal and a constant phase reference signal, an auxiliary source of alternating current, a balanced modulator arranged. tomodulate one of said signals .with the output of said auxiliary source, means for transmitting and receiving the output of said balanced modulator and said other signal, a demodulator'arranged to derive from said modulator output a voltage similar to the signal input to said modulator, and motor control means responsive to the phase relationship between said voltage and said unmodulated signal.

6. A control system including a source of A.-C.

voltage, means connected to said source for deriving, in response to control information to be transmitted, a second A.-C. voltage variable in phase with respect to said first A.-C. voltage; a second source of A.-C. voltage of different frequency from said first and second A.-C. voltages, a balanced modulator, means for applying said variable phase A.-C. voltage and said voltage from said secondsource to said balanced modulator to provide a signal comprising a carrier of the frequency of said second source and sidebands corresponding to said variable phase A.-C. voltage, means for combining said signal with'said first A.-C. voltage to provide a composite signal; means responsive to said composite signal to produce voltages having the same phase relationship to each other as said first and second A.-C. voltages, said last mentioned means comprising a filter connected to separate said first A.-C. voltage from said composite signal, and a demodulator connected to said filter to derive from the remainder of said composite signal an A.-C. voltage corresponding to said second A.-C. voltage.

7. In a remote control system in which control information is derived in the form of two A.-C. voltages of the same frequency but of variable phase with respect to each other, a system for transmitting said information over a single channel including a source of carrier voltage, balanced modulator means for modulating said carrier voltage with one of said A.-C. voltages to provide a suppressed carrier signal including sidebands corresponding to said modulating voltage, means for combining said suppressed carrier signal with the other of said A.-C. voltages to provide a composite signal, and means including a demodulator for deriving from said composite signal two A.-C. voltages having the same phase relationship to each other as said first mentioned two .AJ-C. voltages.

DONALD S. BOND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,183,725 Seeley Dec. 19, 1939 2,236,374 Marrison Mar. 25, 1941 2,256,482 Isbister et a1 Sept, 23, 1941 2,256,487 Moseley et al. Sept, 23, 1941 2,287,002 Moseley June 16, 1942 

